1. Field of the Invention
The present invention relates to the shock-resistant structure for a magnetic disk drive such as a hard disk drive (HDD).
2. Description of the Related Art
In the hard disk drive (HDD), a magnetic disk is enclosed in an enclosure case comprising a base closed by a cover, and driven to rotate by a spindle motor provided in the base. A carriage with a magnetic head is also provided within the enclosure case and freely rotatable and supported through a pivot on the base. The carriage is rotated by an actuator using a voice coil motor (VCM) so that the magnetic head can be positioned over the magnetic disk to perform reading and the like of the magnetic information of the magnetic disk. The carriage is provided with a cantilever suspension having the above-described magnetic head installed on the free end thereof. The suspension is formed into a plate shape so as to be elastically deformable and urges the magnetic head against the magnetic disk. During normal rotation of the magnetic head, the magnetic head floats against the elastic force of the suspension over the magnetic disk. When the rotation of the magnetic disk is stopped or the reading and the like of the magnetic information is not performed, the magnetic head is retracted to the inner peripheral side (parking zone) of the magnetic disk.
Incidentally, on the one hand, the HDD is required to be thin. Since the base is provided with the spindle motor and supports the head arm, it needs thickness to ensure the suitable strength for supporting them. It is therefore preferable that the clearance between the suspension and base be minimized. On the other hand, a portable computer is frequently moved. When it is being moved, it is predictable that the HDD is subjected to shock. Even if the magnetic head were retracted to the parking zone, the above-described suspension has a vibration system such as that shown in FIG. 9, and the magnetic head would swing if the HDD is subjected to shock. The maximum displacement is obtained from Equation (1). EQU .sigma..sub.max =X.sub.max /.omega..sub.n.sup.2 ( 1)
where
.sigma..sub.max : maximum displacement,
X.sub.max =f(.omega..sub.n .multidot..tau..sub.r).multidot.X.sub.0max, ##EQU1##
K=f(K.sub.1, K.sub.2, K.sub.3),
m.sub.1 : magnetic head equivalent mass,
m.sub.2 : suspension equivalent mass,
X.sub.0 : input acceleration, ##EQU2##
.tau.=0.5 to 2 ms,
K.sub.1 =spring constant on the side on which the proximal end of a suspension is supported,
K.sub.2 =spring constant of suspension, and
K.sub.3 =spring constant on the side on which a magnetic disk is supported.
The displacement produced as the suspension is subjected, for example, to an acceleration equivalent to 500 G is shown in FIG. 10. According to this, the longitudinal intermediate portion of the suspension is within a range of 0.5 mm and does not contact with the base, but the free end of the suspension on which the magnetic disk is installed exceeds 0.5 mm and assumes the maximum displacement. The clearance between the suspension in a stationary state (indicated by the solid line) and the base should be minimized as described above. The free end of the suspension crashes against the base under a large acceleration. This crash often destroys the magnetic head. It is also conceivable that the free end of the suspension rebounds due to the reaction of the crash and therefore the acceleration as the magnetic head crashes against the magnetic disk becomes large.
It is conceivable to form a groove 106 in a base 104 between the free end of a suspension 102 and the base 104, as shown in FIG. 11. In the figure, reference numeral 108 denotes a magnetic head. According to this, the contact of the free end of the suspension 102 with the base 104 can be avoided (the stationary state of the suspension 102 is indicated by the solid line and the swing thereof is indicated by the broken line), but, if the displacement becomes large, the magnetic head and the magnetic disk will be damaged because of acceleration.